Method of coating rigid cores

ABSTRACT

Industrial rollers are prepared by photocuring a layer of photocurable composition on the rigid core. As the core cylinder is rotated, a thin layer of photocurable composition is fed intermittently or continuously onto the rotating cylinder, where it can optionally be smoothed by a doctor blade. The photocurable composition preferably is photocured by an ultraviolet light source which is located on the cylinder side opposite the place where the photocurable composition is applied so that premature hardening does not occur in the feed stock. Multiple, consecutive layers of photocurable composition can be built up on the rigid core, each (after the first) being placed upon a partially hardened photocured sublayer. In this manner, the photocured material on the rigid core can be built up to any desired and practical thickness. The photocured surface of the roller can be ground and buffed to make a final product of accurately controlled dimensions.

1451 Oct. 23, 1973 METHOD OF COATING RIGID CORES [75] Inventors: BruceW. Hubbard, Jr., Oak Park,

111.; Clifton L. Kehr, Silver Spring, Md.

[73] Assignee: W. R. Grace & Co., New York,

221 Filed: Nov. 19, 1971 211 Appl. No.: 200,339

Related U.S. Application Data [63] Continuation of Ser. No. 879,175,Nov. 24, 1969,

abandoned.

[52] U.S. Cl. 117/93.31, 117/94, 117/161 UZ, 117/161 ZB, 204/l59.15,260/830 S [51] Int. Cl 344d l/50, C08f l/18, C08f 3/38 [58] Field ofSearch ll7/93.31, 161 R, 117/161'UZ, 161 Z8, 94; 156/272, 446;

[56] References Cited UNlTED STATES PATENTS 1,182,982 5/1916 Crump....118/409 2,270,177 1/1942 Vawryk 118/409 3,361,842 1/1968 Applegath etal. 117 93.31 3,369,922 2/1968 Svrchek 117/94 3,535,193 10/1970 Princell7/93.3l

Oswald et al. 11 7 9331 lhara et al 117/94 Primary ExaminerWilliam D.Martin Assistant Examiner.lohn H. Newsome Att0rney-Virgil H. Marsh etal.

[57] ABSTRACT Industrial rollers are prepared by photocuring a layer ofphotocurable composition on the rigid core. As the core cylinder isrotated, a thin layer of photocurable composition is fed intermittentlyor continuously onto the rotating cylinder, where it can optionally besmoothed by a doctor blade. The photocurable composition preferably isphotocured by an ultraviolet light source which is located on thecylinder side opposite the place where the photocurable composition isapplied so that premature hardening does not occur in the feed stock.Multiple, consecutive layers of photocurable composition can be built upon the rigid core, each (after the first) being placed upon a partiallyhardened photocured sublayer. In this manner, the photocured material onthe rigid core can be built up to any desired and practical thickness.The photocured surface of the roller can be ground and buffed to make afinal product of accurately controlled dimensions.

16 Claims, 6 Drawing Figures PAIENIEBm 23 ms 767 457 sum 1 or 2 III/I IIll/ll mvzmons BRUCE' W. HUBBARD JR. CLIFTON L. KEHR BY MK I ATTORNEYPAIENIEnacImms 3.767.457

SHEET 2 BF 2 INVEN BY M K ATTORNEY BRUCE w. HUB D, CLIFTON L. KE

METHOD OF COATING RIGID CORES This is a continuation, of applicationSer. No. 879,175 filed 11-24-69, now abandoned.

BACKGROUND OF THE INVENTION 1. Objectives of the Invention It is anobject of this invention to prepare and apply coatings to rigid cores.Other objectives will be obvious to those skilled in the art.

2. Prior Art A process is disclosed in U. S. Pat. No. 3,247,012 wherebya continuous coating is applied by brushing, dipping or spraying to anarticle in liquid form, and polymerized in situ by passing the coatingand web under a beam of polymerization effecting electrons from anelectron emitting means. A typical coating composition is a solution ofan unsaturated polyester in a vinyl monomer, which upon copolymerizationforms a crosslinked coating.

Typical means of dip coating a photosensitive layer, e.g., bichromatedgelatin, onto a printing cylinder is given in U. S. Pat. No. 2,357,476.Another typical means of applying photosensitive layers, e.g.,bichromated glue, grum, etc.,- onto a printing cylinder is given in U.S. Pat. No. 2,766,719. This means applies the layer in a conventionalmanner, but drying is required before imaging. In the above process, thephotosensitive layer is exposed imagewise, the image is then developedreliefwise, and the nonimaged areas of the cylinder are etched. U. S.Pat. No. 3,304,909 describes a method for coating cylinders withurethanes which are subsequently subjected to a pressure roller and arecured by heating the entire apparatus contained in an oven for asubstantial period of time after the cylinder has been coated to thedesired thickness. This process has the disadvantage that the feed stockcomposition will also be cured thus causing long delays in cleaning upthe apparatus after each roller coating operation.

Rubber coated rollers for various industrial applications are generallymade by surrounding the cylindrical core with a liquid or solidelastomer in an appropriately-sized cylindrical mold. The mold is heatedat elevated temperatures for long periods of time to vulcanize (or set)the rubber.

BROAD DESCRIPTION OF THE INVENTION Industrial rollers are prepared byplacing a layer of a photocurable composition on a revolving rigid coreand photocuring the layer. The cylinder is rotated at a relatively slowrate of speed, i.e., between about 1 rpm. and the speed at whichcentrifugal force begins to distort the coating before it is photocured.A thin layer of photocurable composition is fed onto the rotatingcylinder, where it can optionally be applied or smoothed by a doctorblade. Liquids of various viscosity ranges or thixotropic pastes arepreferred but with suitable modifications of the feeding mechanism,semi-solid or solid" resinous or elastomeric photocurable compositionscan also be handled without departing from the scope of this invention;the main point is to select a photocurable composition which in thecured state will have the desired physical properties and solventresistance for the intended application that the roller will be usedfor. During the application of the photocurable composition to therotating core, the photocurable composition is intermittently orpreferably continu ously photocured by an ultraviolet light source.Preferably, the U. V. light source is located on the cylinder sideopposite the place where the photocurable composition is applied so thatpremature hardening does not occur in the feed stock, which ismaintained in the shadow cast by the core relative to the UV. lightsource. Multiple consecutive layers of the same or differentphotocurable compositions can be placed on the rigid core, each (afterthe first) being located upon a partially or essentially completelyhardened photo-, cured sublayer. In this manner the photocured materialon the rigid core can be built up to any desired and practicalthickness, say, for example, 2 inches or more. Each layer, as it isapplied, will normally be between about 0.5 and about mils in thicknessalthough this is not critical and may vary greatly depending on thespeed of rotation of the core, the rate of retraction of the doctorblade or feeding from the applicator, the viscosity of the photocurablecomposition, and the curing rate of the photosensitive material. Thephotocured surface on the roller can, if desired, be ground and buffedto help make an end product having an extremely smooth surface and anaccurate, e.g., cylindrical, shape.

An advantage of this invention is that expensive molds or long heatingcycles are not needed to coat a rigid core. The process of thisinvention is quick, convenient and economical, and produces a superior,fully cured product, which usually has an extremely smooth, glaze-likesurface. Post-fabrication curing or aging steps are not required, sincethe application and photocuring to completion (e.g., to constant finalphysical properties) of the photocurable composition is almostsimultaneous and can be carried out under ambient conditions.

DETAILED DESCRIPTION OF THE INVENTION 7 The invention may be moreclearly understood by reference to the following detailed descriptionwhich is non-limiting but which merely exemplifies one of the preferredembodiments:

FIG. 1 is an end view, partially cross-sectional, of the apparatusbefore the coating process commences;

FIG. 2 is the same as FIG. 1 except that the coating process is inprogress;

FIG. 3 is an end view, partially cross-sectional, of another embodimentof the apparatus before the coating process commences;

FIG. 4 is the same as FIG. 3 except that the coating process is inprogress;

FIG. 5 is a transverse cross-sectional view of a coated and photocuredroller; and

FIG. 6 is an end view, partially cross-sectional of another embodimentof this invention with the coating process in progress.

Referring to FIG. 1, roller core 4 rotates in a counterclockwisedirection. The mounting and movingmeans (not shown) for roller core 4 isany conventional device capable of rotating the core about its own axis(e.g., it

is mounted on a lathe). Roller core 4 (1.5 in. dia. by 10 in.) can becleaned before coating, and, in cases of metal rollers comprised ofsteel, can be sand-blasted prior to mounting to remove any rust and toexpose a clean and slightly roughened coating surface. Adhesive bondingagents or primers may be applied if desired to impart good adhesion ofthe photocurable composition to the core surface. Reservoir 8, which maybe heated if desired, contains photocurable composition 12.

(After photocurable composition 12 is prepared, it must be stored in adark area, i.e., in the absence of ultraviolet light.) Delivery tray 16is in a slightly sloping position, with the lower end (delivery lip)about 2 to 20 mils from the surface of roller core 4 during operationand start up (as shown in FIG. 2) and with the upper end (receivingportion) positioned under delivery throat 20 of reservoir 8. A pluralityof delivery throats, etc., can be used to insure that there is coverageover the entire roller length. Photocurable composition 12 is gravityfed down delivery tray 16. Delivery tray 16 is moveable in a horizontalmanner in relationship to roller core 4. Also delivery tray 16 has sidewalls (not shown) to prevent lateral overflow. U.V. light source 24(e.g., one or several 275 watt RS sunlamps; is located so that itsirradiating face is about 1.5 inches from the surface of roller core 4.Several sunlamps can be used, or a long tubular lamp could be used ifdesired. Shield 28 encompasses light source 24, except that slit 32(0.75 in. by in.) allows the ultraviolet light to be beamed directlyonto the surface of roller core 4 without exposing photocurablecomposition 12 in delivery tray 16.

In operation, roller core 4 is typically rotating at about rpm. Valve 36is opened in such a manner as to properly control the amount ofphotocurable composition 12 flowing down delivery tray 16. Light source24 is activated. As photocurable composition 12 contacts the surface ofrotating roller core 4, it adheres thereto as a layer (i.e., coating 40as in FIG. 2). It is seen that since the direction of rotation of rollercore 4 is counterclockwise, the lip delivery tray 16 serves as a doctorblade to control the thickness of the applied coating on each pass.During the coating operation, rolling bank 44 of viscous photocurablecomposition 12 is preferably maintained in the end of delivery tray 16against the surface of core 4. As the uncured coating passes U. V. lightsource 24, it is photocured. The coating thickness can be increased byapplying another coating of uncured photocurable composition 12 onphotocured composition 12 by moving the edge of delivery tray 16 slowlyaway from coated roller core 4. Coating thicknesses as great as about2.0 or more inches can be obtained, and customary total thicknesses upto about 0.5 1.0 inch are easily obtained. After achieving the desiredcoating thickness, delivery tray 16 is retracted away from the coatedsurface of roller core 4. The roller is rotated for several seconds toseveral minutes thereafter to insure a complete photocure of the coatingof photocurable composition 12. The coatings are essentially non-tackyand are usually applied in less than about -30 minutes of totaloperatingtime, depending on the ultimate coating thickness, the intensity of thelight source, etc.

Referring to FIG. 3, a different embodiment of this invention is shown.Roller core 4 and the light source arrangement are the same as inFIG. 1. Reservoir 48 (which may be heated if desired) contains photocurable composition 12, which is dropped onto the top of roller core 4 bymeans of delivery throat 52 during operation and start up (as shown inFIG. 4). The flow rate is controlled by means of valve 56. Scraper 60consists of arm 64, which is pivoted at 68, and scraper blade 72. Arm64, on the other side of pivot 68 from blade 72, is attached to tensionspring 76, which keeps the tip of blade 72 firmly pressed against roller4 as it rotates counterclockwise.

In operation, as best shown in FIG. 4, valve 52 is opened andphotocurable composition flows onto rotating roller 4. Blade 72 forcesphotocurable composition 12 into a smooth layer. Photocurablecomposition 12 is viscous enough to remain in a thin, even layer untilit is photocured by U.V. light source 24. As roller core 4 continues torotate, the thickness of photocured layer builds up. FIG. 5 shows afinished roller (roller core 4 and photocured composition 80) which hasbeen ground and buffed.

The core is typically constructed of a metal, e.g., aluminum, copper,steel, etc., but also can be constructed of a non-metallic substance.The core can be a solid cylinder, a porous sintered cylinder, a hollowpipe or tube, a porous polymeric structure, etc. An example of a porousstructure is a filament wound spindle. Because of the low temperatureand pressure used during the photocuring step, the core can be made frommaterials which cannot withstand the prolonged heating used with heatcurable roller coatings such as those derived from wood, cardboard,synthetic plastics, fiberreinforced composites, foamed resins orelastomers, etc.

The method of applying the photocurable composition to the roller core(cylinder) is not critical, and can also, typically, be a forced-feedmechanism such as the use of a roller transfer to the core, an extrusiontransfer, a curtain coating or knife coating, etc. Also a dip coating orspray coating technique can be used when the photocurable composition isof a relatively low viscosity.

The photocuring means is an actinic radiation source. It can be anultraviolet radiation source that is composed of one or more individualU.V. sources, e.g., a sun lamp, mercury vapor lamp, carbon arc, pulsedxenon arc, etc., several batteries of individual sources, and so forth.Other actinic electromagnetic or actinic ionizing radiation sources canbe used, e.g., electron beams, gamma rays, lasers, visible radiationsources, infrared radiation sources, etc., if the coating composition isformulated properly so that satisfactory rates of curing can be attainedtherewith and if the radiation can be so directed, focussed orcollimated by shielding and the like so as to photocure the coating onthe core but not the feed stream, etc.

The coating substance is preferably a photocurable composition, andparticularly those having elastomeric properties, and particularly thosehaving elastomeric properties in the photocured state. However,photopolymerizable compositions and photocrosslinkable compositions maybeused if the end properties are suitable for the intended rollerapplication. As broadly used in this application, the term photocurableincludes those curing mechanisms which are initiated by actinicelectromagnetic and/or actinic ionizing radiation sources, e.g.,.ultraviolet, visible, infrared radiation, electron beamsfgamma rays,lasers, etc. Combinations of the above forms of radiation also can beused if so desired to obtain special process advantages, and, as amatter of fact, common U.V. light sources emit visible and infraredradiation simultaneously.

Referring to FIG. 6, a different embodiment of this invention is shown.Roller core 4 is the same as in FIG. 1. The photocurable composition 76(optionally without any photocuring rate accelerator) is in a reservoir(not shown) and is delivered to the top of doctor blade 88 via feed line92. Doctor blade 88 is slightly tipped and is similar to delivery tray16 in FIG. 1. The flow rate of composition 16 is controlled by means ofvalve 96. Electron beam source 100 is located above rotating core 4.Radiation shield 104 is positioned as shown in FIG. 6. Mirror 108, onthe back of radiation shield 104, aids the operator in seeing thecoating operation.

The operation shown in FIG. 6 is the same as shown in FIG. 1 and 2except that the photocuring is achieved (operating by remote controls)by means of electron beam source 100. The resultant roller includes core4 and photocured layer 112.

The crucial ingredients in the preferred photocurable composition are: l

1. about 2 to about 98 parts by weight of an ethylenically unsaturatedpolyene (or polyyne) containing two or more reactive unsaturatedcarbon-to-carbon bonds;

2. about 98 to about 2 parts by weight of a polythiol; and

3. about 0.0005 to about 50 parts by weight (based on 100 parts byweight of (1) and (2) of a photocuring rate accelerator.

It is to be understood, however, that when energy sources other thanvisible or ultraviolet light are used to initiate the curing reaction,photocuring rate accelerators (i.e., photosensitizers, etc.) generallyare not required in the formulation. That is to say, the actualcomposition of the photocuring rate accelerator, if required, may varywith the type of energy source that is used to initiate the curingreaction.

The reactive carbon-to-carbon bonds of the polyenes are preferablylocated terminally, near terminally, and- /or pendant from the mainchain. The polythiols, preferably, contain two or more thiol groups permolecule. The photocurable compositions are liquid (i.e., flowable) overthe temperature range provided during the application to the rotatingcore.

Included in the term liquid, as used herein, are those photocurablecompositions which in the presence of inert solvent, aqueous dispersionor plasticizer have a viscosity ranging from slightly above zero to 20million centipoises at 130C. The term liquids includes suspensions, etc.

As used herein polyenes and polyynes refer to simple or complex speciesof alkenes or alkynes having a multiplicity, i.e., at least 2, reactivecarbon-to-carbon unsaturated functional groups per average molecule. Forexample, a diene is a polyene that has two reactive carbon-to-carbondouble bonds per average molecule, while a diyne is a polyyne thatcontains in its structure two reactive carbon-to-carbon triple bonds peraverage molecule. Combinations of reactive carbon-to-carbon triple bondswithin the same molecule are also operable. An example of this ismonovinylacetylene, which is a polyeneyne under our definition. Forpurposes of brevity all these classes of compounds will be referred toherein as polyenes.

As used herein the term reactive unsaturated carbon-to-carbon groupsmeans groups which will react under proper conditions as set forthherein with thiol groups to yield the thioether linka e mat ascontrasted to the term unreactive carbon-tocarbon unsaturation whichmeans groups when found in aromatic nuclei (cyclic structuresexemplified by benzene, pyridine, anthracene, and the like) which do notunder the same conditions react with the thiols to give thioetherlinkages. In the instant invention products from the reaction ofpolyenes with polythiols which contain 2 or more thiol groups peraverage molecule are called polythioether polymers or polythioethers.

Methods of preparing various polyenes, with the limitations set forthherein, useful within the scope of this invention are disclosed incopending application Ser. No. 674,773, filed Oct. 12, 1967, nowabandoned. and assigned to the same assignee. Some of the usefulpolyenes are prepared in the detailed examples set forth in thefollowing specification. The general formulas for several, useful,representative polyenes and polyynes are given in the Figure in Dutch(Holland) Application No. 67/ 10439 which was laid open to publicinspection and copying thereof on Jan. 29, 1968 (said pertinent portionsof said public document being incorporated herein by reference).

One group of polyenes, with the limitations set forth herein, operablein the instant invention is that taught in a copending applicationhaving Ser. No. 617,801, inventors: Kehr and Wszolek, filed: Feb. 23,1967, now abandoned and assigned to the same assignee. This groupincludes those having a molecular weight in the range of 50 to 20,000, aviscosity ranging from 0 to 20 million centipoises at 70C. of thegeneral formula: [A]-(X),,,, wherein X is a member of the groupconsisting of and R-C E C; m is at least 2; R is independently selectedfrom the group consisting of hydrogen, halogen, and an organic compoundselected from the group consisting of aryl, substituted aryl,cycloalkyl, substituted cycloalkyl, aralkyl, substituted aralkyl, alkyland substituted alkyl groups containing one to four carbon atoms; and Ais a polyvalent organic moiety free of l) reactive carbon-to-carbonunsaturation and (2) unsaturated groups in conjugation with the reactiveene or yne groups'in X. Thus A may contain cyclic grouplings and minoramounts of hetero atoms such as N, S, P or 0 but contains primarilycarbon-carbon, carbonoxygen or silicon-oxygen containing chain linkageswithout any reactive carbon-to-carbon' unsaturation. This grouppreferably has a molecular weight over 300.

In this first group, the polyenes are simple or complex species ofalkenes or alkynes having a multiplicity of pendant, terminally or nearterminally positioned reactive carbon-to-carbon unsaturated functionalgroups per average molecule. As used herein for determining the positionof the reactive functional carbonto-carbon unsaturation, the termterminal means that said functional unsaturation is at an end of themain chain in the molecule; whereas by near terminal is meant that thefunctional unsaturation is not more than four carbon atoms away from anend of the main chain in the molecule. The term pendant means that thereactive carbon-to-carbon unsaturation The liquid polyenes operable inthis first group contain one or more of the following types ofnon-aromatic and non-conjugated reactive carbon-to-carbon unsaturation:

(5) LLC (1) -CH=CH- 2 -c E c- (6) 'iz saz:

3 -CH=CH2 7 -CH=(]} 4 -c E cu s A ba n2 '7 These functional groups asshown in 1-8 supra are situand the like, so as to form a conjugatedsystem of unsatuaated bonds exemplified by the structure:

Bill,

etc. On the average the polyenes must contain 2 or more reactiveunsaturated carbon-to-carbon bonds per molecule and a have a viscosityin the range from slightly above to about 20 million centipoises at 70C.Included in the term polyenes as used herein are those materials whichin the presence of an inert solvent, aqueous dispersion or plasticizerfall within the viscosity range set out above at 70C. Operable polyenesin the instant invention have molecular weights in the range of about 50to about 20,000, preferably about 500 to about 10,000.

Examples of operable polyenes from this first group include, but are notlimited to:

l. Crotyl-terminated polyurethanes which contain two reactive" doublebonds per average molecule in a near terminal position of the averagegeneral formula:

wherein at is at least 1.

2. Ethylene/propylene/non-conjugated diene terpolymers, such as Nordell040 manufactured by E. l. du- Pont de Nemours & Co., Inc., whichcontains pendant reactive" double bonds of the formula: --Cl-l- ,CH=CHCH 3. The following structure which contains terminal reactive" doublebonds:

wherein at is at least 1.

4. The following structure which contains near terminal reactive" doublebonds:

wherein x is at least 1.

A second group of polyenes operable in this invention includes thosepolyenes in which the reactive unsaturated carbon-to-carbon bonds areconjugated with adjacent unsaturated groupings. Examples of operableconjugated reactive ene systems include but are not limited to thefollowing:

new,saigswaais A few typical examples of polymeric polyenes whichcontain conjugated reactive double bond groupings such as thosedescribed above are poly(oxyethylene) glycol (600 M.W.) diacrylate;poly(oxytetramethylene) glycol 1,000 M.W.) dimethacrylate; thetriacrylate of the reaction product of trimethylol propane with 20 molesof ethylene oxide; and the like.

As used herein, the term polythiols refers to simple or complex organiccompounds having a multiplicity of pendant or terminally positioned SHfunctional groups per average molecule.

On the average the polythiols must contain 2 or more SH groups permolecule. They usually have a viscosity range of slightly above 0 toabout 20 million centipoises (cps) at C., as measured by a BrookfieldViscometer. Included in the term polythiols as used herein are thosematerials which in the presence of an inert solvent, aqueous dispersionor plasticizer fall within the viscosity range set out above 70C.Operable polythiols in the instant invention usually have molecularweights in the range about 50 to about 20,000, or more, preferably aboutto about 10,000.

The polythiols operable in the instant invention can be exemplified bythe general formula: R,,(SH),,, wherein n is at least 2 and R, is apolyvalent organic moiety free from reactive carbon-to-carbonunsaturation. Thus R may contain cyclic groupings and minor amounts ofhetero atoms such as N, S, P or 0 but primarily containscarbon-hydrogen, carbon-oxygen, or silicon-oxygen containing chainlinkages free of any reactive carbon-to-carbon unsaturation.

One class of polythiols operable with polyenes in the instant inventionto obtain essentially odorless compositions are esters ofthiol-containing acids of the general formula: HSR -COOH, wherein R,, isan organic moiety containing no reactive carbon-to-carbon unsaturationwith polyhydroxy compounds of the general structure: R (Ol-l), wherein Ris an organic moiety containing no reactive carbon-to-carbonunsaturation and n is 2 or greater. These components will react undersuitable conditions to give a polythiol having the general structure:

I 9 R.-(O ELEV-SH) wherein R and R are organic moieties containing noreactive carbon-to-carbon unsaturation and n is 2 or more.

Certain polythiols, such as-the aliphatic monomeric polythiols (ethanedithiol, hexamethylene dithiol, decamethylene dithiol,totylene-2,4-dithiol, etc.), some polymeric polythiols, such as athiol-terminated ethylcyclohexyl dimercaptan polymer, etc., and similarpolythiols which are conveniently and ordinarily synthesized on acommercial basis, although having obnoxious odors, are operable in thisinvention. Examples of the polythiolcompounds preferred for thisinvention because of their relatively low odor level and fast curingrate include but are not limited to esters of thioglycolic acid (HS-CHCOOH),a-mercaptopropionic acid (HS-Cl-l(Cl-l )-COOH) and B-mercaptopropionic acid (HS-CH CH COOH) with polyhydroxy compounds such asglycols, triols, tetraols, pentaols, hexaols, etc. Specific examples ofthe preferred polythiols include but are not limited to ethylene glycolbis(thioglyco-- late), ethylene glycol -bis(B-mercaptopropionate),trimethylolpropane tris(thioglycolate), trimethylolpropanetris(B-mercaptopropionate), penetaerythritol tetrakis(thioglycolate) andpentaerythritol tetrakis(fimercaptopropionate), all of which arecommercially available. A specific example of a preferred polymericpolythiol is poly(propylene ether) glycol. bis(B-mercaptopropionate)which is prepared from poly(propylene ether) glycol (e.g., PluracolP2010, Wyandotte Chemical Corp.) and B-mercaptopropionic acid byesterification.

The preferred polythiol compounds are characterized by a low level ofmercaptan-like odor initially, and after reaction give essentiallyodorless cured polythioether end products which are commercially usefulresins or elastomers for roller coatings.

As used herein the term fodorless means the substantial absence of thewell-known offensive and sometimes obnoxious odors that arecharacteristic of hydrogen sulfide and the derivative family ofcompounds known as mercaptans. g

The term functionality as used herein refers to the average number ofene or thiol groups per molecule in the polyene and/or the polythiol.For example, a triene is a polyene with an average of three reactivecarbon-to-carbon unsaturated groups per molecule and thus has afunctionality of 3. A dithiol is a polythiol with an average oftwo'thiol groups per molecule and thus has a functionality of 2.

It is further understood and implied in the above definitions that inthese systems the functionality of the polyene and the polythiolcomponent is commonly expressed in whole numbers although in practicethe actual functionality may be-fractional. For example, a polyenecomponent having a nominal functionality of 2 (from theoreticalconsiderations alone) may in fact have an effective functionality ofsomewhat less than 2. Such a product is useful in the instant inventionand is referred to herein as having a functionality of 2.

To obtain the maximum strength, solvent resistance, creep resistance,heat resistance and freedom from tackiness, the reaction componentsconsisting of the polyenes and polythiols of this invention generallyare formulated in such a manner as to give solid, crosslinked, threedimensional network polythioether polymer systems or curing. In order toachieve such infinite network formation, the individual polyenes andpolythiols must each have a functionality of at least 2 and the sum ofthe functionalities of the polyene and polythiol components must alwaysbe greater than 4. Blends and mixtures of the polyenes and thepolythiols con taining said functionality are also operable herein.

The preferred photocuring reaction can be initiated by U.V. radiationcontained in actinic radiation from sunlight or obtained from speciallight sources which emit significant amounts of U.V. light. (Useful U.V.radiation generally has a wavelength in the range of about 2,000 toabout 4,000 angstrom units.) Thus it is possible merely to expose thepolyene and polythiol admixture to actinic radiation under ambientconditions or otherwise and obtain a cured solid elastomeric or resinousproduct useful as a core coating material. But this approach to theproblem results in extremely long exposure times which cause the processin the vast bulk of applications to be commercially unfeasible. Chemicalphotocuring rate accelerators (photoinitiators or photosensitizers orphotoactivators) e.g., quinone, methyl ethyl ketone, etc., serve todrastically reduce the exposure time and thereby when used inconjunction with various forms of energetic radiation (containing U.V.radiation) yield very rapid, commercially practical photocures by thepractice of the instant invention. Useful photocuring rate acceleratorsinclude benzophenone; acetophenone; acenapthene-quinone;

methyl ethyl ketone; thioxanthen-9-one; xanthen-' 9-one; 7-H-Benz [de]anthracen-7-one; dibenzosuberone; l-naphthaldehyde;4,4'-bis(dimethylamino) benzophenone; fluorene-9-one; l-acetonaphthone;2'- acetonaphthone; 2,3-butanedione; anthraquinone; lindanone;2-tert-butyl anthraquinone; valerophenone; hexanophenone;S-phenylbutyrophenone; p-morpholinopropiophenone;4-morpholinobenzophenone; 4-morpholinodesoxybenzoin; p-diacetylbenzene;4- aminobenzophenone; 4'-methoxyacetophenone; benz' aldehyde;a-tetralone; 9-acetylphenanthr'ene; 2- acetylphenanthrene;IO-thioxanthenone; 3- acetylphenanthrene; 3-acetylindole; 1,3,5-triacetylbenzene; etc.; and blends thereof. The photoinitiators areadded in an amount ranging from about 0.0005 to about 50 percent byweight of the polyene and polythiol components in the instant invention.Benzophenone is the preferred photocuring rate accelerator.

The compositions to be photocured, i.e., converted to roller corecoatings, in accord with the present invention may, if desired, includesuch additives as antioxidants, inhibitors, activators, fillers,pigments, dyes, antistatic agents, flame-retardant agents, thickeners,thixotropic agents, surface-active agents, viscosity modifiers,plasticizers, and the like within the scope of this invention. Suchadditives generally are preblended with the polyene or polythiol priorto impregnating it in and/or on the ultimate structure. The aforesaidadditives may be present in quantities up to 500 parts or more per partsphotocurable composition by weight and preferably 0.0005 to 300 parts onthe same basis. The type and concentration of the additives must beselected with great care so that the final composition remainsphotocurable under conditions of exposure.

The compounding of the components prior to photocuring can be carriedout in any conventional'manner which takes into account that thematerial is sensitive to U.V. radiation. This composition generally canbe stored in the dark for extended periods of time prior to actual useor even incorporation in and/or on the ultimate structure.

It is often desirable to place a suitable anti-oxidant, e.g., 1onol",hydroquinone, t -butyl catechol, etc., in the photocurable composition.These agents in optimum amounts will help to stabilize the fullyformulated composition against premature thickening or curing duringperiods of storage prior to use in the coating process.

The following examples will aid in explaining, but should not be deemedas limiting, the instant invention. In all cases, unless otherwisenoted, all parts and percentages are by weight.

EXAMPLE 1 3456.3 gm. (1.75 mole) of poly(propylene ether) glycol,commercially available under the trade name PPG 2025 from Union Carbide,and 1.7 gm. of di-nbutyl tin dilaurate were placed in a 5-liter,roundbottom, 3-neck flask. The mixture in the flask was degassed at 1 C.for one hour and was then cooled to 25C. by means of an external waterbath. 207 gm. (3.50 moles) of allyl alcohol, with stirring, were addedto the flask. 609.0 gm (3.50 moles) of an 80 to 20 percent isomermixture of tolylene-2,4-diisocyanate and totylene-2,6-diisocyanate,respectively, sold under the trade name Mondur TD 80, was charged to theflask. The mixture was stirred will. The flask was cooled by the waterbath during this period. Eight minutes after the Mondur TD 80 was added,the temperature of the mixture was 59C. After 20 minutes, the NCOcontent was 12.39 mg. NCO/gm; after 45 minutes, it was 9.87 mg. NCO/gm.;and after 75 minutes, it was 6.72 mg. NCO/gm. The water bath was removed80 minutes after the Mondur TD 80 had been added, the tempperature ofthe mixture being 41C., and heat was applied until the mixturetemperature reached 60C. That temperature was maintained. 105 minutesafter the Mondur TD 80 was added, the NCO content was 3.58 mg. NCO/gm;after 135 minutes,it was 1.13 mg. NCO/gm; and after 195 minutes, it was0.42 mg. NCO/gm. At that point in time, the resultant polymercomposition was heated to 70C., and vacuum-stripped for 1 hour. Theresultant polymer composition was labeled composition 1, and had aviscosity of 16,000 cps. as measured on a Brookfield Viscometer at 30C.Unless otherwise stated, all the viscosity measurements were made on aBrookfield Viscometer at 30C.

The above procedure was repeated five times, and resultant compositionswere labeled compositions 2 to 6, respectively. The heating step lasted180 minutes, 140 minutes, 205 minutes and 180 minutes, respectively.With composition 2, the temperature was 60C. after 8 minutes; withcomposition 3, the temperature was 57C. after 6 minutes; withcomposition 4, the temperature was 41C. after 20 minutes, at which timethe temperature was raised and held at 60C.; with composition 5, thetemperature was 57.5C. in 8 minutes, was 42C. in 40 minutes, then takenup to 60C. and lowered to 58C. after 120 minutes; and with composition6, the temperature was 57C. in 6 minutes, and was 41C. after 60 minutes,at which time the temperature was immediately raised to 60C. Theviscosity of the resultant polymer compositions was 15,500 cps.; 16,000

cps.; 17,000 cps.; 16,800 cps.; and 16,200 cps. respectively.

Compositions 1,2,3,4,5, and 6 were placed in a 6- gallon container andstirred well. The resultant polymer composition had a viscosity of16,000 cps. and the NCO content was 0.01 mg. NCO/gm. This compositepolymer composition was labeled polymer A, which has the followingapproximate structure:

parts of polymer A, 10 parts of polythiol A, 1.5 parts of benzophenoneand 0.1 part by weight of lonol were thoroughly admixed. This resultedin photocurable composition A. Polythiol A was pentaerythritoltetrakis(B-mercaptopropionate), which is commercially available underthe trade name Q-43 Ester (sold by Carlisle Chemical Company). lonol isa table designation for 2,6-di-tert-butyl-4- methylphenol (stericallyhindered) and is commercially available from Shell Chemical Company.lonol has good anti-oxidant properties, is nonirritating to the skin,and has a comparatively inert, non-acidic hydroxyl group.

Photocurable composition A was placed in a reservoir like the one shownin FIG. 1. The rest of the experiment was similar to that shown in FIG.1 and the accompanying write-up above. The end of the delivery tray wasplaced about 20 mils away from the roller core (steel). The roller corewas rotated at 25 r.p.m. The valve on the throat of the reservoir wasopened. As the coating was applied to the roller core, the delivery traywas slowly moved (manually) away from the core. When the coatingthickness reached about one-fourth inch, the delivery tray wascompletely backed away from the coated roller. The coated roller wasfurther rotated for 3 minutes before the U.V. lamp was turned off. Theresultant photocured coating was smooth and had a glaze-like finish. Thefinal hardness of the coating was measured at Shore A 30 (ASTM). Atypical segment of the three dimensional crosslinked, polythioetherproduct is:

ClIa

EXAMPLE 2 Example 1 was repeated except that parts of polythiol A wasused. The resultant photocured coating was smooth and had a glaze-likefinish.

EXAMPLE 3 to 6 EXAMPLE 7 Example 1 was repeated, except that half of thepentaaerythritol tetrakis (B-mercaptopropionate) was replaced with 5parts of ethylene glycol bis(B-mercaptopropionate). The resultantphotocured coating was smooth and had a glaze-like finish.

EXAMPLE 8 Example 1 was repeated except that 60 parts of polymer C wasused in place of polymer A. Polymer C was prepared as follows: 458 gm.(0.23 mole) of a commercially available liquid polymeric diisocyanatesold under the trade name Adiprene L-100 by E. l. duPont de Nemours &Co. was charged to a dry resin kettle maintained under a nitrogenatmosphere and equipped with a condenser, stirrer, thermometer, and gasinlet and outlet. 37.8 gm. (0.65 mole) of allyl alcohol was charged tothe kettle and the reaction was continued for 17 hours with stirring at100C. Thereafter the nitrogen atmosphere was removed and the kettle wasevaculated 8 hours at 100C. 50 cc. dry benzene was added to the kettleand the reaction product was azeotroped with benzene to remove theunreacted alcohol. This allyl-terminated liquid polymer had a molecularweight of approximately 2100 and was labeled polymer C The resultantphotocured coating was smooth and had a glaze-like finish.

EXAMPLE 9 Example 1 was repeated except that 100 parts of polymer D wasused in place of polymer A. Polymer D was prepared as follows: 1,500 gm.(0.47 mole) of a linear solid polyester diol having a molecular weightof 3 ,200 and commercially available from Hooker Chemical Corp. underthe trade name Rucoflex S-101 1-35 was charged to a 3-liter, 3-neckedflask and heated to l 10C. under vacuum and nitrogen for 1 hour withstirring. 83 gm. of allyl isocyanate having a molecular weight of 83.1and commercially available from Upjohn Co. was added to the flask alongwith 0.3 cc. of dibutyl tin dilaurate (catalyst), commercially availablefrom J. T. Baker Co. The reaction was continued at 110C. with stirringfor 1 hour. This allyl-terminated polymer was labeled polymer D.

The resultant photocured coating was smooth and had a glaze-like finish.

EXAMPLE 10 to 15 Example 1 was repeated six times, except that thebenzophenone was replaced with cyclohexanone (2.0 parts) (Example 10),acetone (1 part) (Example 11), acetophenone (0.3 part) (Example 12),dibenzosuberone (0.5 part) (Example 13), a blend of acetone (0.3 part)and p-diacetylbenzene (0.6 part) (Example 14), and 3-acetylphenanthrene(1 part) (Example 15), respectively. The resultant photocured coatingswere smooth and had glaze-like finishes.

EXAMPLES 16 Example 1 was repeated twice, except that the roller corewas constructed of copper (Example 16) and fiberglass reinforcedpolyester resin (Example 17), respectively. The resultant photocuredcoatings were smooth and had a glaze-like finish.

Example 18 This example illustrates the use of a monomeric polythiol anda monomeric polyene. 23.8 gm. of pentaerythritoltetrakis(B-mercaptopropionate); 25.6 gm. of the reaction product of onemole of 1,4-butanediol with two moles of allyl isocyanate; and 0.5 gm.of benzophenone were thoroughly admixed. Example 1 was repeated, exceptthat the above photocurable composition was used in place ofphotocurable composition A. The resultant photocured coating was smooth,hard and had a glaze-like finish.

EXAMPLE 19 This example illustrates the use of a reactive ene groupconjugated with another double bond grouping (C=O). 27 gm. of thetriacrylate of the reaction product of one mole of trimethylol propanewith 20 moles of ethylene oxide; 9 gm. of pentaerythritol tetrakis(/3-mercaptopropionate); and 0.5 gm. of benzophenone were thoroughlyadmixed. Example 1 was repeated, except that the above photocurablecomposition was used in place of photocurable composition A. Theresultant photocured coating was smooth and had a glaze-like finish.

EXAMPLE 20 This example illustrates the use of photocurable compositioncontaining a monomeric polyene and a polymeric polythiol. 50 gm. of DionPolymercaptan Resin DPM-1002, which is a thiol terminated liquid polymerhaving a functionality of 2 to 3 and a molecular weight of about 5000and commercially available from Diamond Alkali Company; 2.5 gm. oftriallyl cyanurate; and 0.5 gm. of benzophenone were admixed. Example 1was repeated, except that the above photocurable composition was used inplace of photocurable composition A. The resultant photocured coatingwas smooth and had a glaze-like finish.

EXAMPLE 21 This example illustrates the use of a photocurablecomposition containing a polymeric polyene and a polymeric polythiol.Example 1 was repeated, except that the photocurable compositioncontained 50 parts of the polymeric polyene used in Example 8; parts ofthe polymeric polythiol used in Example 20; and 0.5 part ofbenzophenone. The resultant photocured coating was smooth and had aglaze-like finish.

EXAMPLE 22 Photocurable composition A was placed in a reservoir like theone shown in FIG. 3. The rest of the experimental set-up was similar tothat shown in FIG. 3 and the accompanying write-up above about theset-up in FIG. 3. The roller core (one in. dia.) was rotated at 15r.p.m. The valve on the throat of the reservoir was opened. When thecoating thickness reached a little over one inch, the flow of thephotocurable composition was completely turned off. Blade 72 was backedaway from roller 4. The coated roller was further rotated for 3 minutesbefore the UN. lamp was turned off. The resultant photocured coating wassmooth and had a glaze-like finish, but was ground and buffed to supplya matte surface.

EXAMPLE 23 Photocurable composition X was prepared by admixing 100 partsof polymer A, 10 parts of polythiol A and 0.l part of lonol.Photocurable composition X was placed in a reservoir and fed to doctorknife 4 via feed line 92 as shown in FIG. 6. Photocurable composition Xwas coated on rotating core 4. Doctor blade 88 was retracted at a rateof 0.01 inch per revolution of roller core 4. Roller core 4 (a 4 inchdiameter steel roller) was rotated at 10 r.p.m. Electron beam source wastuned on as the coating started. Electron beam source was a 500 kwinsulated core transformer commercially available from High VoltageEngineering Co. After the coating and irradiation had proceeded for 5minutes, the feed of photocurable composition X was stopped. After thephotocurable composition X in the bank of the doctor rod had beenconsumed, as observed through mirror the electron beam irradiation wascontinued for 1 minute to assure complete cure of surface layer of theroller. When roller was removed it was found that coated photocurablecomposition X was cured to an elastomer and that the surface was smooth.The roller was ground to a 5.00 inch O.D. roller of good quality.

It is claimed:

1. A process for preparing a coated cylindrical core which comprises:

a. admixing a photocurable composition consisting essentially ofabout2-98 parts by weight of an ethylenically unsaturated polyene containing2 or more reactive unsaturated carbon to carbon bonds per molecule,about 98 to about 2 parts by weight of polythiol containing 2 or morethiol groups per molecule, the total combined functionality of thereactive unsaturated carbon to carbon bonds per molecule in the polyeneand the thiol groups per molecule in the polythiol being greater than 4,and about 0.0005 to about 50 parts by weight based on 100 parts byweight of the polyene and polythiol of a photocuring rate accelerator;

. applying said photocurable composition uniformly to the surface on aline parallel to the longitudinal axis of a rotating cylindrical core togradually build up layer by layer a coating on said core; and

. curing said photocurable composition coating on said rotatingcylindrical core, whereby said curing is achieved by subjecting saidphotocurable composition to actinic or electron beam radiation.

2. A process as described in claim 1 wherein said photocuring isachieved by means of ultraviolet radiation.

3. A process as described in claim 1 wherein said photocuring isachieved by means of electron beam radiation.

4. A process as described in claim 1 wherein said coating and saidphotocuring occur simultaneously, said photocuring occurring in thefreshly coated layer and in previously coated layers present.

5. A process as described in claim 1 wherein said photocurablecomposition comprises an ethylenically unsaturated polyene having atleast two reactive ene groups per molecule, a polythiol containing twoor more thiol groups per molecule, and a photocuring rate accelerator,where the sum of the functionalities of said polyene and said polythiolis greater than four.

6. A process as described in claim 5 wherein the photocurablecomposition in said photocurable layer is comprised of 2 to 98 parts byweight of said polyene, 98 to 2 parts by weight of said polythiol, and0.0005 to 50 parts by weight photocuring rate accelerator based on 100parts by weight of said polyene and said polythiol.

7. A process as described in claim 6 wherein said polyene compositionhas a molecular weight in the range of 50 to 20,000; has a viscosityranging from essentially 0 to 20,000,000 centipoises at 130C; and has ageneral formula: [A](X),, wherein X is a member of the group consistingof- Eli.

and R-C E C; m is an integer of at least two; R is independentlyselected from the group consisting of hydrogen, halogen, and an organiccompound selected from the group consisting of aryl, substituted aryl,aralkyl, substituted aralkyl, cycloalkyl, substituted cycloalkyl, alkyland substituted alkyl groups containing one to four carbon atoms; and Ais a polyvalent polymeric organic moiety free of (l) reactivecarbon-to-carbon unsaturation, and (2) unsaturated groupings in terminalconjugation with X.

8. A process as described in claim 7 wherein the polyene has a molecularweight in excess of 300.

9. A process as described in claim 7 wherein the two or more reactiveene groups are located terminally in the molecule, or where the two ormore reactive ene groups are conjugated with other unsaturated groups.

10. A process as described in claim 7 wherein the said polythiol has amolecular weight between about 50 and about 20,000, and has a viscositybetween slightly above zero and about 20,000,000 centipoises at C.

11. A process as described in claim 7 wherein said polyene is preparedfrom allyl alcohol, polyalkylene ether glycol and tolylene diisocyanate.

12. A process as described in claim 6 wherein the photocurablecomposition contains 0.0005 to 5.0 parts by weight of an antioxidant,0.05 to 25 parts by weight of a pigment, 1.0 to 50 parts by weight of aplasticizer, and 0.5 to parts by weight of a filler, each of saidingredients being based upon 100 parts by weight of said polyene andsaid polythiol.

13. A process as described in claim 9 wherein said antioxidant is2,6-di-tert-butyl-4-methylphenol.

14. A process as described in claim 1 wherein said photocured coating isground and buffed.

15. A process as described in claim 1 wherein said radiation iseelectron beam radiation from a source coated onto said rotating corefrom a source which is located at a point opposite the radiation source.

16. An article of manufacture consisting of a cylindriwhich is locatedessentially perpendicular of said rotat- 5 cal core coated with a curedPolythioethering core and wherein photocurable composition is

2. A process as described in claim 1 wherein said photocuring isachieved by means of ultraviolet radiation.
 3. A process as described inclaim 1 wherein said photocuring is achieved by means of electron beamradiation.
 4. A process as described in claim 1 wherein said coating andsaid photocuring occur simultaneously, said photocuring occurring in thefreshly coated layer and in previously coated layers present.
 5. Aprocess as described in claim 1 wherein said photocurable compositioncomprises an ethylenically unsaturated polyene having at least tworeactive ene groups per molecule, a polythiol containing two or morethiol groups per molecule, and a photocuring rate accelerator, where thesum of the functionalities of said polyene and said polythiol is greaterthan four.
 6. A process as described in claim 5 wherein the photocurablecomposition in said photocurable layer is comprised of 2 to 98 parts byweight of said polyene, 98 to 2 parts by weight of said polythiol, and0.0005 to 50 parts by weight photocuring rate accelerator based on 100parts by weight of said polyene and said polythiol.
 7. A process asdescribed in claim 6 wherein said polyene composition has a molecularweight in the range of 50 to 20,000; has a viscosity ranging fromessentially 0 to 20,000,000 centipoises at 130*C.; and has a generalformula: (A)-(X)m wherein X is a member of the group consisting of
 8. Aprocess as described in claim 7 wherein the polyene has a molecularweight in excess of
 300. 9. A process as described in claim 7 whereinthe two or more reactive ene groups are located terminally in themolecule, or where the two or more reactive ene groups are conjugatedwith other unsaturated groups.
 10. A process as described in claim 7wherein the said polythiol has a molecular weight between about 50 andabout 20,000, and has a viscosity between slightly above zero and about20,000,000 centipoises at 70*C.
 11. A process as described in claim 7wherein said polyene is prepared from allyl alcohol, polyalkylene etherglycol and tolylene diisocyanate.
 12. A process as described in claim 6wherein the photocurable composition contains 0.0005 to 5.0 parts byweight of an antioxidant, 0.05 to 25 parts by weight of a pigment, 1.0to 50 parts by weight of a plasticizer, and 0.5 to 100 parts by weightof a filler, each of said ingredients being based upon 100 parts byweight of said polyene and said polythiol.
 13. A process as described inclaim 9 wherein said antioxidant is 2,6-di-tert-butyl-4-methylphenol.14. A process as described in claim 1 wherein said photocured coating isground and buffed.
 15. A process as described in claim 1 wherein saidradiation is electron beam radiation from a source which is locatedessentially perpendicular of said rotating core and wherein photocurablecomposition is coated onto said rotating core from a source which islocated at a point opposite the radiation source.
 16. An article ofmanufacture consisting of a cylindrical core coated with a curedpolythioether.